1. Field of Invention
The invention relates generally to waste recovery and recycling, and specifically to a process for transforming pre-used asphaltic roofing shingles into paving bricks.
2. Background of the Invention
Up to 11 million tons of asphaltic roofing shingles are disposed of annually in North America. Possibly 20% of this material comprises unused shingle manufacturing waste that can be incorporated into hot-mix asphalt. The remaining 8 million tons is pre-used weathered shingles called ‘tearoffs’.
A small but growing quantity of these pre-used shingles is being comminuted and used in several applications such as low-value suppressant of dust on minor roads and parking lots; as aggregate in road construction and maintenance; as an additive both to cold and hot mix paving asphalt; and in the manufacture of hot-molded paving bricks or blocks.
The bulk of the 8 million tons is, however, land filled.
No product has been manufactured through compression of cold shingle particles to the best knowledge of the inventor. U.S. Pat. No. 6,039,914 awarded to Gehrke in 2000 indeed explicitly excludes that possibility. The inventor, however, has invented a suitable shredder and discovered mold release agents. Their novelty enables advantageous cold-shredding and cold-forming of bricks from shingles. In combination they represent a novel process.
The transformation of asphaltic shingles into products requires skill in the two arts of comminution and of subsequent aggregation or dissolution into a mix. It is a characteristic of asphalt that its viscosity decreases with increasing temperature. Therefore those skilled in the prior art appreciate that in general shingle comminution requires low temperatures in order to prevent the material from aggregating and sticking to the equipment, while the aggregation of shingle particles or their dissolution into a mix requires heat.
The heating of asphalt is costly. It also becomes sticky, hard to handle, and potentially harmful as it releases particulate matter and reactive organic gasses, possibly including volatile organic compounds. The avoidance of heat is therefore an obvious advantage.
Ford, U.S. Pat. No. 1,290,954 of 1919 was the first to patent a method of reclaiming unused asphalt shingles. He taught chilling or freezing the material prior to grinding, and molding the particles through pressure at an undisclosed temperature into products such as waterproof containers. Ford rejected previous attempts to add hot solvent to comminuted shingles due to high demands for power and heat. Contemporary grinders would have been of the type patented by Hull, U.S. Pat. No. 194,776 of 1877, using cooperating hammers or ‘rubbers’ attached to a cylinder and concave as in an agricultural thresher.
Robinson, U.S. Pat. No. 1,732,281 of 1929 invented a process of transforming small, unused shingle trimmings and punchings from manufacturing waste that avoided the need for comminution. He designed a screw apparatus with a succession of shearing actions to heat and agglomerate the material at temperatures as high as 265° F. (129° C.) into a plastic mass suitable for forming into products.
Minge et al, U.S. Pat. No. 2,368,371 in 1945 taught a method of comminuting unused shingles in a series of three high speed hammer mills, successively fitted with finer screens of 1½ inch, ¾ inch and ¼ inch. The first two mills operated at 1,850 rpm and the third at 3,500 rpm. To avoid the inherent problem of material heating and machine blockage, limestone was fed with the shingles into the second mill, while forced air provided additional cooling in the third mill. The particles were then mixed with asphalt heated to 500° F. (260° C.) to make a material suitable for use in the manufacture of shingles.
Schweigert et al, U.S. Pat. No. 3,664,592 in 1972 proposed a low-speed granulating or shearing device with any number of cooperating knives fitted with a piercing-cutting tooth mounted on two counter-rotating shafts. The low speed of 20 to 50 rpm avoided the problem of heating, but left relatively large pieces of shingle requiring further reduction in a high-speed hammer-mill. A patent for such a process was awarded to Drouin in 1992—see below.
Good, deceased et al, U.S. Pat. No. 4,222,851 in 1980 taught a method of recovering components from comminuted unused manufacturing waste shingles by solvent extraction at temperatures between 80 and 125° C. (176 to 257° F.) and at pressures between 5 and 100 p.s.i. This formed a miscella that was separated using evaporative techniques.
Babus, U.S. Pat. No. 4,325,641 in 1982 proposed the agitation of non-comminuted new manufacturing waste shingles in soft asphaltic oil at 300° F. (149° C.) to make a mix suitable for paving.
Brock, U.S. Pat. No. 4,706,893 in 1987 taught the combining of comminuted new and pre-used shingles into a hot-mix paving composition. Hot particles were added to appropriate quantities of liquid asphalt and aggregate, or of reclaimed roadway material. The proportion of shingles was limited by the capacity of the softest asphalt with a high penetration number of 250 to offset the hard asphalt in new shingles with a low penetration number of 11 and reach the standard penetration number of 50 to 60 for asphalt in hot-mix paving. The limit for adding shingles, some of which comprise 52% asphalt, was calculated to be within the range of 2 to 8%. This varied according to (a) the hardness of the added liquid asphalt, (b) on the proportion of asphalt in the shingle material, (c) its hardness, and (d) on the amount of recycled roadway with a hardness of 30 to 50. Brock also taught the use of a hog or hold-down conveyor invented by Knight, U.S. Pat. No. 3,825,192 in 1974. This controlled the flow of shingles into the hammer mill to avoid overloading. Brock, U.S. Pat. No. 5,201,472 in 1993 proposed a method of preparing shredded shingles for later use in a form that resisted sticking together.
Drouin et al, U.S. Pat. No. 5,098,025 in 1992 proposed fine comminution of pre-used and unused asphalt shingles achieved through successive reduction in a shredder and hammer mill. Water or solvent was added to prevent heating and aggregation. The liquid was then mixed with other slurries to create a pulp that was suitable for cold forming into asphalt fiberboard, or as a damp-proof coating.
Gaudio, U.S. Pat. No. 5,221,338 and U.S. Pat. No. 5,223,032 in 1993 proposed cold mixing of roughage derived from crushed concrete with recycled roadway in appropriate ratios with comminuted pre-used shingles and light oil. The product was used for pavement construction and repair.
Richards, U.S. Pat. No. 5,221,702 in 1993 invented a method of hot molding an interlocking paving brick of 200×100×60 mm or 80 mm (8×4×2.5 inches or 3 inches) from a mixture of recyclables such as polyethylene bottles, tires and pre-used shingles, with asphalt comprising 40% by volume. The mixture was heated to a temperature of 325 to 375° F. (163 to 191° C.) and compressed at a pressure of 750 psi, with the hot mold submerged in cold water. Richards, U.S. Pat. No. 5,367,007 in 1994 taught a process for manufacturing a multi-layered composite block from the same material.
Grzybowski U.S. Pat. No. 5,236,497 in 1993, taught how to use a mixture of comminuted new and pre-used asphalt shingles as the dominant, and possibly sole, source of bitumen in a cold-patch material suitable for pavement repairs.
Chiovitti, U.S. Pat. No. 5,337,965 in 1994 invented a way of mechanically recovering and separating the asphalt/fiber and aggregate components of new and pre-used shingles by agitating comminuted shingles in a water tank.
Omann, U.S. Pat. No. 5,340,038 in 1994 proposed a comminutor comprising a plurality of cutter bars to kick, pull apart, cut and shear material such as wood, concrete and new and pre-used shingles aggregated in substantial clumps. Gross particles were produced requiring further reduction in a hammer mill. See below the patent awarded to Omann.
Glynn, U.S. Pat. No. 5,344,485 in 1994 taught a method of preparing a cold emulsion of asphalt, water, pumice, soap, and caustic soda in which to suspend, separate and mix aggregate with comminuted shingles and other recyclables such as shredded tires, plastics and glass, together with soils contaminated with petroleum or other hazardous materials. The proportion of shingles was 4 to 6% by weight. The product was a cold-mix concrete that set after expelling the water under pressure.
Omann, U.S. Pat. No. 5,385,426 in 1995 proposed using the comminutor patented by his brother (see above) to reduce shingles to large pieces that were further reduced in a succession of modified hammer mills cooled by compressed air or alternatively with water. The particles were then heated by microwaves to 200° F. (93° C.) for use in patching or paving roadways, or packaged for home use.
Pavelek, U.S. Pat. No. 5,511,899 in 1996 taught a method of laying down a road surface comprising conventionally comminuted pre-used shingles sandwiched between two layers of aggregate.
Chivers, U.S. Pat. No. 5,626,659 in 1997 proposed a method of reducing new and pre-used asphalt shingles to fine particles. Clogging of the comminutor was avoided by adding limestone or dolomite to shingles in any ratio up to 100:56. This permitted temperatures in the hammer mill to reach 300° F. (149° C.) without the material aggregating or sticking to the machinery.
Zickell et al, U.S. Pat. No. 5,848,755 in 1998 taught a method of heating uncomminuted asphalt shingles to about 350° F. (177° C.) in a milling apparatus and mixing in virgin liquid asphalt. The resulting paste could be poured or pumped for undisclosed uses.
Gehrke et al, U.S. Pat. No. 6,039,914 in 2000 disclosed a process for producing a paver measuring 4×8×2½ inches. He heated comminuted new and pre-used shingles under infrared heaters to a temperature of 130 to 150° F. (54 to 66° C.), and fed them into an extruder. The output was molded in two stages separated by a critical delay at a pressure of 60 tons, or the equivalent of 4,125 psi. Gehrke stated that an inferior and brittle block could be produced by pressure alone without heat, and that excessive heat decomposed part of the asphalt to ash that was brittle when aggregated.
Deschamps and Hanus, Canadian Pat. No. 2,148,878 in 2001 proposed a high-speed shredder that pulled shingles or other material downwardly through preferably three successive pairs of counter-rotating, intermeshing blades or knives within a housing. This reduced the material into successively smaller pieces quickly and without heating and without the use of sieves or grates. The design offered relatively simple and inexpensive construction with superior performance. This shredder forms an integral part of the process specified in this application.
Petermeier, U.S. Pat. No. 6,497,930 in 2002 taught how to form an interlocking paving brick from comminuted new and pre-used shingles heated to a temperature of 215 to 275° F. (102 to 135° C.) and pressed in a heated mold at a pressure of 300 to 760 psi.
Mischo, U.S. Patent Application Publication No. US2002/0011687A1 in 2002 proposed the comminution of shingles on a small scale with a conventional hammer mill. The output was sieved. The larger particles were used as material input for one product, while the remaining particles were heated to a temperature between 200 and 300° F. for extrusion and hot-molding into bricks and similar products.
With the sole exception of the Deschamps' shredder, these processes taught in the prior art are associated with various difficulties and disadvantages;
a. The processes taught by Babus and Brock for mixing treated asphalt shingles into hot mix asphalt composition limited the shingle proportion to 8%, and typically to 1%. The asphalt in new shingles, at times comprising 500% of the shingle by weight, was too hard (low penetration) for use in a hot mix containing only 6% asphalt. Furthermore only new shingles could be used because in pre-used shingles the asphalt was further oxidised and hardened to varying and unpredictable degrees by exposure to UV and air. Babus used only new shingles. Brock incorporated pre-used shingles, but compensated for their hardness by adding an offsetting quantity of soft high penetration asphalt. In practice the incorporation of pre-used shingles in hot-mix is difficult, complicated and severely limited. None of these factors applies in this application.b. Conventional comminutors screen the particles internally by grinding and regrinding them until they are reduced sufficiently to pass through the sieve or grate. This action heats the material, which becomes plastic, and increases power consumption. The plastic material agglomerates and adheres to the machinery, eventually blocking the screen. The material then backs up, overheats, and stops the machine. The material cools to a rock-hard consistency that is difficult and time-consuming to remove. These difficulties are explained in Omann U.S. Pat. No. 5,385,426 in 1995 and Chivers, U.S. Pat. No. 5,626,659 in 1997. This application teaches how to avoid such problems.c. Feeding a hammer mill with shingles that are clumped together can overload the shredder, as explained in Brock, U.S. Pat. No. 4,706,893 in 1987. He alleviated the problem by incorporating a hog. Such a device is not required in this application.d. Some, including Omann, U.S. Pat. No. 5,385,426 in 1995, and Drouin et al, U.S. Pat. No. 5,098,025 in 1992, proposed the use of two comminutors; a slow-speed shredder for gross reduction and a high-speed hammer mill for fine reduction. The consequence was increased capital investment and maintenance, which are avoided in this application.e. Drouin et al, U.S. Pat. No. 5,098,025 in 1992 proposed cooling shingles in the comminutor with water. This method is in common use today. For example, the HC 2400B hammer mill manufactured by Peterson Pacific Corp for comminuting wood, operates at 2,100 rpm with ½-inch grate. It is modified for use in shingles with strengthened cutters and larger water lines. However wet particles must be dried before being adding to hot asphalt because of the dangers associated with steam, which is explosive in the confines of a mold. The complication and cost of drying do not apply in this application.f. Draining wet shredded particles and drying them in a heated rotating drum was proposed by Richards, U.S. Pat. No. 5,221,702 in 1993, by Gehrke et al, U.S. Pat. No. 6,039,914 in 2000, and by Petermeier, U.S. Pat. No. 6,497,930 in 2002. This created polluted water that could concern the regulatory authority, and influence their willingness to issue a certificate of approval. No discharges result from this application.g. As an earlier alternative to cooling water, Minge et al, U.S. Pat. No. 2,368,371 in 1941 proposed blending the shingles with up to 20% sand or screenings to prevent agglomeration in the comminutor. This added material cannot however be separated out and is economical only when needed in the final product. The additional material increases the load on the comminutor and reduces the capacity to reduce shingles. No such disadvantage accompanies this application.h. Another method for reducing heat build-up in the comminutor was to remove the screens and sieve the particles separately. Unacceptably large particles were returned to the front of the machine repeatedly until of the desired size. The percentage of such returns could be large, but are minor in this application.i. The use of comminuted shingles as road aggregate, dust suppressant or as an additive to hot-mix asphalt has relatively low added value compared with the paving bricks and other products described in this application.j. The need to maintain the heated shingle particles at a minimum of 212° F. (100° C.) required heating the weighing container and mold. This added cost and complication that are avoided in this application.k. Gehrke et al, U.S. Pat. No. 6,039,914 in 2000, proposed a two-step compaction process with a delay of minutes between the steps. This added complication and reduced productivity. The factor is absent from this application.l. Gehrke et al, U.S. Pat. No. 6,039,914 in 2000 taught the heating of particles to 130 to 150° F. (54 to 66° C.) and applying a pressure of 60 tons or 4,125 p.s.i. By contrast, in this application the particles are at ambient temperature and the pressure applied is substantially greater than 5,000 p.s.i., and preferably about 11,500 p.s.i.m. Gehrke et al, U.S. Pat. No. 6,039,914 in 2000 stated that an inferior and brittle block could be produced by pressure alone without heat. It is assumed they referred to a pressure of 4,125 p.s.i., which is substantially lower than the process pressure used in this application.n. Petermeier, U.S. Pat. No. 6,497,930 in 2002 proposed molding a brick at temperatures of 215 to 275° F. (102 to 135° C.) in a mold hotter than the particles. Even so, a low friction surface to prevent the plastic material from adhering to the mold was proposed in certain circumstances. This application avoids special surfaces and high temperatures.
In the preceding, the products into which shingles have been recycled relate almost entirely to road building, to road maintenance, or to formed and molded paving products, which is the subject of the present invention. The methods previously taught have employed temperatures ranging from 135° F. (54° C.) to 375° F. (191° C.), and pressures between 200 and 4,125 p.s.i. Only Gehrke et al, U.S. Pat. No. 6,039,914 in 2000 described the cold molding of paving bricks, which is the subject of the present invention, but explicitly rejected it for reasons including product performance.